lib: Allow hexdump to be used in SPL

It is sometimes useful to output hex dumps in SPL. Add a config option to
allow this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>

lib/Kconfig

@@ -542,6 +542,14 @@ config HEXDUMP
 	help
 	  This enables functions for printing dumps of binary data.
 
+config SPL_HEXDUMP
+	bool "Enable hexdump in SPL"
+	depends on HEXDUMP
+	default y
+	help
+	  This enables functions for printing dumps of binary data in
+	  SPL.
+
 config OF_LIBFDT
 	bool "Enable the FDT library"
 	default y if OF_CONTROL